1. Field of the Invention
The present invention relates to systems for the removal of fouling materials such as seaweed and eel grass that can clog the intakes of jet drives. More particularly, the present invention relates to a cutting assembly arranged to resist separation from the intake grate of a jet drive. The present invention also relates to a cutting blade positioned adjacent to the impeller of the jet drive to provide improved cutting capability for the system to remove fouling from the jet drive impeller.
2. Description of the Prior Art
Watercraft have traditionally been, and primarily are, propelled through water by propellers. An alternative propulsion mechanism gaining interest is the water-jet drive. Water-jet drive systems provide a number of advantages over propeller-driven systems. They eliminate a number of support and attachment components, such as rudders, propeller shafts, propellers, that increase vessel drag and limit shallow water passage. Moreover, they are safer for people and marine life in proximity to the stern of the vessel in that the moving parts are located within the hull envelope. They also tend to be quieter than propeller systems and maneuverability is enhanced at all speeds. Water-jet drives also tend to provide increased fuel economy. For these and other reasons, the water-jet drive has become increasingly popular as a watercraft propulsion system.
Water-jet drive systems propel watercraft by rapidly accelerating a relatively small volume of water over a distance. This is accomplished using one or more impeller stages located within the watercraft hull. The impeller includes a plurality of blades confined in a housing. Rotation of the impeller blades draws water into an intake of the housing, past the blades, and through an outlet at the stem. The housing is ordinarily designed to direct flow such that the water is expelled above the waterline of the watercraft. The housing may be tapered toward the outlet to increase water acceleration and maximize thrust. Improved propulsion efficiency occurs when there is a close fit between the ends of the impeller blades and the interior of the housing.
An important aspect in the effective operation of the water-jet drive is the availability of an adequate supply of water to be expelled from the housing outlet. For that reason, in general, a larger intake is desirable as it ensures a greater water supply available to the impeller to generate thrust. On the other hand, a large intake allows the impeller to draw debris in with the water. It is desirable to minimize debris contact with the impeller, which debris may damage or destroy the blades or clog the impeller. It is therefore useful to avoid or minimize drawing into the housing debris of any size or type that will cause damage or fouling of the impeller while keeping the intake as open as possible.
Manufacturers of watercraft using water-jet drives place intake grates at the housing intake to catch relatively large-sized debris and prevent such debris from reaching the impeller. In relatively clear water, these grates serve their purpose adequately. However, when the watercraft passes through patches of heavy debris—seaweed and eel grass in particular—the grate is overwhelmed and the intake is substantially blocked. In other instances, this type of debris or fouling passes through the grate and then sticks to the front leading edges of the blades of the impeller within the housing. Either type of fouling results in a substantial reduction of thrust capability and corresponding slowing or halt to movement of the watercraft. Unexpected substantial slowing or halting of the watercraft can be a serious safety issue for the watercraft operator and occupants, dependent upon sea conditions, weather and location.
Water-jet drive watercraft operators resolve such fouling problems in several ad hoc ways. First, they may reverse the direction of rotation of the impeller to force the fouling to move away from the intake in the hope that it will be dislodged from the grate. Second, they attempt to access the housing through an observation port below the deck and try to pull out any fouling contained therein. Third, they may be forced to jump into the water, swim under the watercraft, and pull the fouling away from the grate by hand. These options are either ineffective or an undesirable way to solve the problem. Examples of described devices can be found in U.S. Pat. Nos. 6,482,055; 6,183,319; and 6,083,063. However, these devices and the ad hoc techniques described above fail to address adequately the problem of fouling removal in water-jet drives. Worse, these ad hoc methods and described devices require that the watercraft be completely stopped before they can be performed or used. Therefore, not only are they ineffective at removing debris, they interrupt an otherwise enjoyable sail. When they must be performed or used repeatedly, which is often the case, given their ineffectiveness, the sailing experience can be ruined entirely. In order to reverse the impeller to “backflush” the water-jet drive housing in the hope of dislodging the debris on the grate, it is necessary to have a transmission coupled to the impeller to effect that reversal. The transmission is a costly and heavy component that must also be maintained. It would be preferable to avoid addition of a transmission for the purpose of changing impeller rotation.
U.S. Pat. No. 7,377,826 describes a system capable of removing fouling materials from the intake of a water-jet drive. That system provides a fouling removal system that may be incorporated into existing water-jet drive structures or incorporated into new construction. Further, that fouling removal system may be operated automatically using a control device in proximity to other control devices of the watercraft. Still further, that fouling removal system does not require the inclusion of a transmission to enable impeller rotation changes. Yet further, that fouling removal system includes a secondary mechanism for removing debris fouling the impeller blades of a water-jet drive. Even further, that fouling system is capable of removing debris from the intake grate and impeller of a water-jet drive while a watercraft is stationary or is operating at any speed, including full speed.
However, the fouling removal system described in U.S. Pat. No. 7,377,826 has certain features that limit the optimization of its performance characteristics. First, the mechanism for cutting the debris from the grate of the propulsion system may not be able to cut through large bunches of seaweed as the bulk of the blockage forces the blade to ride over the seaweed. Also, high water flow rates through the grate may cause the blade to lift as it is actuated. In both instances, in sufficient quantities of seaweed or eel grass are sheared. In particular, the degree and frequency of blade lifting away from the grate may increase with increased seaweed bulk and/or when the boat is traveling at high speeds. Second, the actuation mechanism of the existing system is positioned at least partially in the flow path of water passing through the grate. That positioning can be a point of debris retention that cannot be resolved with the cutter. It also creates turbulence, which can create noise as well as lessen the efficiency of the water-jet drive. Third, the passive cutter stud of the system described in U.S. Pat. No. 7,377,826 has shown effective removal of debris located on or near the impeller, but there remains some seaweed clogging near the shaft of the impeller. It would be preferable to be remove all, or substantially all, such debris from the impeller including near the impeller shaft. Fourth, it can be difficult to place the passive cutter stud sufficiently close to the impeller to enable effective debris removal at that location.